3.31 gears with taller tires

[R66SS427]

I know its not optimal but my truck(2011 sb/cc) came with 3.31 gears. Has anybody put a taller tire on and what effect did it have on power? I'm thinking maybe a 285/70/17. 33 " tall.
Thanks in advance

 

[DaveBen]

You increase your gear ratio ( lower numbers ). Less pick up and a little more top end (if that applies). What truck are you talking about? I can't think of a Super Duty that has 3.31's. Are you sure?

Dave

 

[Fine69]

Dave, SRW Super Duty's have 3.31 or 3.55 gears now, started in 2010 because the 6.4 fuel mileage sucked so bad.

 

[DaveBen]

Thank you Fine69. I am surprised that Ford went up to 3.31. I can see 3.55.

Dave

 

[WD40]

I am not impressed with the tall gears, 3.73 is the lowest gear you can get in a 2011 and 20012 F-350
now and I have always liked a 4.10 for pulling my 16+ fifthwheel. Looks like the 3.31 would be slow on
the take off. Top in would be nice. When you add the tires you going to be around a 2.78 rear gear.
Doug

 

[R66SS427]

I understand the ratio changes with the tire diameter, I was just wondering if anybody had done it with this setup. Is the 6 sp auto in the 6.7 geared differently? It seems to accellerate fine in stock form. I don't want to kill the trucks performance but those stock tires belong on a VW bug.

 

[jpringle83]

Yes the 6.7 6spd auto is geared differently than say the 5spd auto that I have in my 6.0 so the effects of a taller tire won't be quite as noticeable. My question for you is what size is your stock tire? My '05 came with a metric 33.2in tire and all the 4x4 6.7s I have seen have nearly a 34in tire. Your truck must be 4x2 please fill out your signature so we know what you have. Click on USER CP then edit signature.

 

[jpringle83]

Ok so I just looked it up your stock tire should be 265/70R17 which measures 31.6". I did a similar jump from a 275/70R18 stock tire to a 35x12.50R20 on my truck and it ends up being roughly 8 revolutions a mile less. I see no problem with that difference. There's no lugging of the engine or anything like that so I say go ahead and do it. I just checked to see if anything had changed and apparently if your truck had come with the 18" wheel you would have gotten the larger tire like mine did. I just find that weird that they wouldn't try to keep the 17,18 and 20 inch wheels tire diameter closer.

 

[JLDickmon]

yeah, 8 revs per mile ain't jack... that's the difference between a new tore and a worn one..